1. Technical Field
This invention relates to optical devices, and more particularly, to telescopes capable of operating in the infrared frequency spectrum.
2. Discussion
There is a need for telescopes capable of operating over a wide band of infrared radiation. Two of the bands of particular interest are the medium infrared (IR) band having wavelengths of from 3.8 to 5.0 micrometers and the long IR band having wavelengths of from 8 to 11.5 micrometers. These two bands correspond to regions of high transmittance within the atmosphere. Such telescopes can be used with a forward-looking infrared (FLIR) scanner and imager systems. Other applications of such a telescope would include infrared search-track (IRST) sensors and dual-band, target-recognition systems.
Previously known dual-band or wide-band infrared telescope designs typically used toxic materials such as KRS-5 and As.sub.2 S.sub.3 or exotic materials such as potassium bromide, CdTe, GaAs or CsI. It was heretofore believed that it was necessary to employ these hard-to-use materials in order to correct chromatic aberrations in both spectral bands.